Apparatus for measuring hemoglobin concentration and oxygen saturation thereof

ABSTRACT

A light beam having a first wavelength (λ 1 ) is applied to the blood from a first light radiation section, while a light beam having a second wavelength (λ 2 ) is applied from second and third light radiation sections different in positions from the first radiation section and from each other to the blood and the respective reflected-light intensity (I 1 , I 2 , I 3 ) is detected. A first correction value (X) for correcting the reflected-light intensity ratio (I 2  /I 3 ) is calculated by a first correction value operation section (40) and a second correction value (C 1 ) is calculated by a second correction value operation section (42) by use of this first correction value and the reflected-light intensity (I 3 ). The reflected-light intensity ratio (I 1  /I 2 ) is corrected by use of this second correction value and an oxygen saturation in the blood is operated based on correlation function by use of the corrected reflected-light intensity ratio (R s ). The reflected-light intensity ratio (I 2  /I 3 ) is corrected by the coefficient of correction thus operated and the hemoglobin concentration in the blood is operated based on correlation function by use of the reflected light intensity ratio thus corrected.

TECHNICAL FIELD

This invention relates to an apparatus for measuring hemoglobinconcentration and hemoglobin oxygen saturation, which apparatus utilizesthe extinction characteristics of hemoglobin in blood to measure thehemoglobin concentration in blood as well as the degree to whichhemoglobin is saturated with oxygen.

BACKGROUND ART

Conventionally, measurement of hemoglobin concentration in blood isperformed by hemolyzing sampled blood physically or chemically,introducing the sample to a cuvette and irradiating it with light of aspecific wavelength, measuring the transmitted light and calculating thehemoglobin concentration using the Lambert-Beer law. With an apparatusand method for measuring the degree of oxygen saturation in hemoglobincontained in blood, the blood is irradiated with light having twowavelengths λ₁, λ₂, the intensity of the reflected light is measured,and the degree of oxygen saturation is determined from the followingequation:

    SO.sub.2 =A+B×(I.sub.2 /I.sub.1)

where I₁, I₂ represent the intensities of the reflected light at therespective wavelengths λ₁, λ₂, and A, B are constants.

A problem with the above-described method of measuring hemoglobinconcentration in blood is that continuous measurement is difficult sinceit is necessary to hemolyze the blood measured. In addition, a problemwith the above-described method of measuring the degree of oxygensaturation of hemoglobin is that the results of measuring oxygensaturation are prone to error owing to the significant influence ofphysiological factors in blood, especially hematocrit value (theproportion of blood occupied by red blood cells). More specifically, theextinction (reflection) characteristics of blood vary depending uponabsorption and scattering caused by pigments and particles contained inthe blood. In particular, as shown in FIG. 13, light-absorptioncoefficient varies greatly depending upon the state of bonding betweenhemoglobin and oxygen and the wavelength of the irradiating light. HereHbO₂ represents oxygenated hemoglobin, Hbr represents reducedhemoglobin, and HbCO stands for carbomonoxyhemoglobin.

In the vicinity of a wavelength of 800 nm, Hb0₂ and Hbr intersect andthe light absorbancies are equal, as will be understood from thesedrawings. This wavelength is referred to as a point of equal absorption.This indicates a wavelength at which light absorbancy is not changed bythe degree of oxygen saturation of hemoglobin.

FIGS. 14A and 14B are graphs in which the relationship betweenreflected-light intensity at wavelengths of 660 nm and 800 nm,respectively, and the degree of oxygen saturation is plotted whilevarying the hematocrit value (HCT) and hemoglobin (Hb) concentration.The blood sample used here was bovine blood.

In the case of the wavelength of 660 nm shown in FIG. 14A, the lightabsorbancy of oxygenated hemoglobin is small in comparison with that ofreduced hemoglobin. Consequently, reflected-light intensity increaseswith a rise in the degree of oxygen saturation. In the case of thewavelength of 800 nm shown in FIG. 14B, it will be understood that achange in degree of oxygen saturation does not have much influencebecause this wavelength is the equal absorption point. Furthermore, itwill be understood from FIGS. 14A, 14B that reflected-light intensitydecreases with a decrease in the hematocrit value at each wavelength.

It should be noted that these measurements of reflected-light intensityare results obtained upon previously calibrating each reflected-lightintensity to a predetermined value using a white reflector.

FIG. 15 illustrates the relationship between degree of oxygen saturationcalculated using the foregoing equation and degree of oxygen saturationmeasured using an OSM2 hemoxymeter (manufactured by Radiometer) frommeasured values of reflected-light intensity at wavelengths 660 nm and800 nm shown in FIGS. 14A, 14B, respectively. As a result, the degree ofoxygen saturation calculated from the foregoing equation is profoundlyinfluenced by the hematrocrit value in the region of low oxygensaturation, and a large error develops in the calculated value of oxygensaturation. Furthermore, in the prior art, the degree of oxygensaturation in blood cannot be measured accurately in continuous fashionwithout being influenced by the hematrocrit value.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide an apparatus formeasuring degree of oxygen saturation, in which an accurate degree ofoxygen saturation can be obtained without the influence of hematocritvalue even in a region of low oxygen saturation.

Another object of the present invention is to provide an apparatus formeasuring degree of oxygen saturation, in which the degree of oxygensaturation of hemoglobin can be measured continuously without theinfluence of the hematrocrit value.

A further object of the present invention is to provide an apparatus formeasuring hemoglobin concentration, in which blood can be measuredcontinuously and without hemolysis.

In order to solve the foregoing objects of the present invention, thereis provided an apparatus for measuring the degree of saturation ofoxygen in hemoglobin, comprising first light-irradiating means forirradiating blood with light of a first wavelength, second and thirdlight-irradiating means for irradiating the blood with light of a secondwavelength different from the light of the first wavelength, detectingmeans provided so as to be at different distances from the secondlight-irradiating means and third light-irradiating means for detectingintensities of light reflected from the blood irradiated with the lightfrom the first light-irradiating means, second light-irradiating meansand third light-irradiating means, first corrective value calculatingmeans for calculating a first corrective value which corrects a ratio ofthe reflected-light intensity, which results from irradiation by thesecond light-irradiating means and is detected by the detecting means,to the reflected-light intensity, which results from irradiation by thethird light-irradiating means and is detected by the detecting means,second corrective value calculating means for calculating a secondcorrective value using the first corrective value and thereflected-light intensity of light from the third light-irradiatingmeans detected continuously by the detecting means, reflected-lightintensity ratio correcting means for correcting, by using the secondcorrective value, a reflected-light intensity ratio of thereflected-light intensity of light from the first light-irradiatingmeans detected continuously by the detecting means to thereflected-light intensity of light from the second light-irradiatingmeans detected continuously by the detecting means, and oxygensaturation degree calculating means for calculating degree of oxygensaturation in blood based on a correlation function using the correctedreflected-light intensity ratio outputted by the reflected-lightintensity ratio correcting means.

Further, the foregoing objects are attained by an apparatus formeasuring the degree of saturation of oxygen in hemoglobin, comprisingfirst light-irradiating means for irradiating blood with light of afirst wavelength, second and third light-irradiating means forirradiating the blood with light of a second wavelength different fromthe light of the first wavelength, detecting means provided so as to beat different distances from the second light-irradiating means and thirdlight-irradiating means for detecting intensities of light reflectedfrom the blood irradiated with the light from the firstlight-irradiating means, second light-irradiating means and thirdlight-irradiating means, first corrective value calculating means forcalculating, from a reference value of hemoglobin concentration and aknown value of hemoglobin concentration, a first corrective value forcorrecting a ratio of reflected-light intensities of light from thesecond and third light-irradiating means detected by the detectingmeans, second corrective value calculating means for calculating asecond corrective value using the first corrective value and thereflected-light intensity of light from the third light-irradiatingmeans detected continuously by the detecting means, reflected-lightintensity ratio correcting means for correcting, by using the secondcorrective value, a reflected-light intensity ratio of thereflected-light intensity of light from the first light-irradiatingmeans detected continuously by the detecting means to thereflected-light intensity of light from the second light-irradiatingmeans, and oxygen saturation degree calculating means for calculatingdegree of oxygen saturation in blood using the corrected reflected-lightintensity ratio outputted by the reflected-light intensity ratiocorrecting means.

Further, the foregoing objects are attained by an apparatus formeasuring hemoglobin concentration, comprising first and secondlight-irradiating means for irradiating blood with light of a specificwavelength, detecting means provided so as to be at different distancesfrom the first light-irradiating means and second light-irradiatingmeans for detecting intensities of light reflected from the bloodirradiated with the light from the first and second light-irradiatingmeans, corrective coefficient calculating means for calculating acorrective coefficient which corrects a ratio of the reflected-lightintensity of light from the first light-irradiating means to thereflected-light intensity of light from the second light-irradiatingmeans, these light intensities being detected by the detecting means,reflected-light intensity ratio correcting means for correcting, byusing the corrective coefficient, a reflected-light intensity ratio ofthe reflected-light intensity of light from the first light-irradiatingmeans detected continuously by the detecting means to thereflected-light intensity of light from the second light-irradiatingmeans, and hemoglobin concentration calculating means for calculatinghemoglobin concentration in blood based on a correlation function usingthe corrected reflected-light intensity ratio outputted by thereflected-light intensity ratio correcting means.

In accordance with the present invention, the light-irradiating meanscan be reduced in size by making common use of both a light-emittingsource and a light-irradiating unit.

In accordance with the present invention, a portion in contact with theblood can be completely insulated by connecting the light-emittingsource and the light-irradiating unit with an optical fiber.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a first embodiment of an apparatus formeasuring degree of oxygen saturation according to the presentinvention;

FIG. 2 is an end view showing an example of a sensor probe used in theembodiment of the apparatus for measuring degree of oxygen saturation;

FIG. 3 is a sectional view of a connector to which the sensor probeshown in FIG. 2 is attached;

FIG. 4 is a block diagram showing a specific example of a firstcorrective value calculating unit in the block diagram of FIG. 2;

FIG. 5 is a block diagram of a second embodiment of an apparatus formeasuring degree of oxygen saturation according to the presentinvention;

FIG. 6 is a block diagram showing a specific example of a firstcorrective value calculating unit in the block diagram of FIG. 4;

FIG. 7 is a flowchart showing a method of measuring degree of oxygensaturation by the apparatus for measuring degree of oxygen saturationaccording to the first embodiment;

FIG. 8A and 8B are flowcharts showing a method of measuring degree ofoxygen saturation by the apparatus for measuring degree of oxygensaturation according to the another embodiment;

FIG. 9 is a flowchart showing a method of measuring degree of oxygensaturation by the apparatus for measuring degree of oxygen saturationaccording to the second embodiment;

FIG. 10 is a view showing the relationship between degree of oxygensaturation obtained by the apparatus for measuring degree of oxygensaturation according to an embodiment and degree of oxygen saturationmeasured by an OSM2 hemoxymeter for purposes of contrast;

FIG. 11 is a view showing the relationship between degree of oxygensaturation obtained by the apparatus for measuring degree of oxygensaturation according to the first embodiment and degree of oxygensaturation measured by an OSM2 hemoxymeter for purposes of contrast;

FIG. 12 is a view showing the relationship between degree of oxygensaturation obtained by the apparatus for measuring degree of oxygensaturation according to an embodiment of a second invention of thepresent application and degree of oxygen saturation measured by an OSM2hemoxymeter for purposes of contrast;

FIG. 13 is a view showing a common extinction characteristic of blood;

FIGS. 14A and 14B are diagrams in which the relationship betweenreflected light intensities at wavelengths of about 660 nm and about 800nm, respectively, is plotted while varying the hematocrit value (HCT);

FIG. 15 is a diagram showing the relationship between degree of oxygensaturation obtained by a conventional method of measuring degree ofoxygen saturation and degree of oxygen saturation measured by an OSM2hemoxymeter for purposes of contrast;

FIG. 16 is a block diagram of an apparatus for measuring hemoglobinconcentration according to another embodiment of the invention;

FIG. 17 is a block diagram showing a specific example of a correctivecoefficient calculating unit in the block diagram of FIG. 16;

FIG. 18A and 18B are flowcharts showing a method of measuring hemoglobinconcentration by an apparatus for measuring hemoglobin concentrationaccording to an embodiment of the invention;

FIG. 19 is a diagram showing a extinction characteristic of hemoglobinmeasured by an OSM2 hemoxymeter for purposes of contrast with hemoglobinconcentration obtained by an embodiment of the apparatus for measuringhemoglobin concentration according to the present invention;

FIGS. 20 and 21 are diagrams in which is plotted the relationshipbetween reflected-light intensity and hemoglobin concentration whenblood is irradiated with light having a wavelength of about 800 nm, withdistance being varied; and

FIG. 22 is a diagram showing the relationship between a ratio I₁ /I₂ andhemoglobin concentration, in which I₁ represents reflected-lightintensity when the distance between received light and emitted light is0.25 mm, and I₂ represents reflected-light intensity when the distancebetween received light and emitted light is 0.50 mm.

BEST MODE FOR CARRYING OUT THE INVENTION

The best for carrying out the invention will now be described in detailwith reference to the accompanying drawings.

As shown in FIG. 1, an apparatus for measuring the degree of oxygensaturation of hemoglobin includes a light-irradiating circuit 1, adetecting unit 2 for detecting the intensity of light reflected fromblood irradiated with light from the light-irradiating circuit 1, acorrecting unit 3 which corrects for the influence of hematocrit value,a unit 4 for calculating the degree of oxygen saturation using theoutput of the correcting unit 3, and a display unit 5 for displaying theoutput of the oxygen saturation calculating unit 3.

The light-irradiating circuit 1 has a first light-irradiating unit forirradiating the blood with light of a first wavelength, a secondlight-irradiating unit for irradiating the sample with light of a secondwavelength different from the light of the first wavelength, and thirdlight-irradiating means for irradiating the blood with light of thesecond wavelength.

In the arrangement shown in FIG. 1, the first light-irradiating unit andthe second light-irradiating unit are constituted by a firstlight-emitting source for emitting light of the first wavelength, asecond light-emitting source for emitting light of the secondwavelength, a common light-irradiating unit for irradiating the bloodwith the light from the first light-emitting source and secondlight-emitting source, and a third light-irradiating unit forirradiating the blood with light of the second wavelength.

More specifically, the light-irradiating circuit 1 comprises alight-emitting source and a light-irradiating unit for irradiating theblood with light from the light-emitting source. The light-emittingsource comprises three light-emitting diodes 11, 12, 13. Thelight-emitting diode 11 emits light having a wavelength of about 660 nm(λ₁), and the light-emitting diodes 12, 13 each emit light having awavelength of about 800 nm (λ₂). The light emitting diodes 11, 12, 13are arranged so as to emit light alternately by being driven through adriver circuit 15 to which pulses of a predetermined interval and pulsewidth are applied by a pulse generator 14 so as not to overlap in time.The light emitted by the light-emitting diode 11 and the light emittedby the light-emitting diode 12 passes through a photocoupler 17 and alight-emitting optical fiber 18a to irradiate the blood from alight-irradiating portion 20 formed by the end face of the optical fiber18a. By adopting such an arrangement, a single light-irradiating portion20 suffices and the apparatus can be made small in size. In addition,the irradiating portion for light of wavelength λ₁ from thelight-emitting diode 11 and the irradiating portion for light ofwavelength λ₂ from the light-emitting diode 12 can be placed at the samedistance from the detecting unit, described below.

The light emitting by the light-emitting diode 13 passes through alight-emitting optical fiber 18b to irradiate the blood from alight-irradiating portion 19 formed by the end face of the optical fiber18b.

The invention is not limited to the arrangement shown in FIG. 1, for itis permissible to adopt an arrangement in which the light-irradiatingcircuit 1 is composed of three light-emitting sources and threelight-irradiating portions for irradiating the blood with the light fromrespective ones of the light-emitting sources, or in which thelight-irradiating circuit 1 is constituted by a light-emitting sourcefor emitting the light of the first wavelength, a light-irradiatingportion for irradiating the blood with the light from thislight-emitting portion, a shared light-emitting source for emittinglight of the second wavelength, and two light-irradiating portions forirradiating the blood, from different positions, with light from thislight-emitting source.

The detecting unit 2 is for detecting the intensity of the light, whichis emitted by the light-irradiating circuit 1, after the light isreflected from the blood. In the arrangement shown in FIG. 1, aphotodetecting portion 21 of the detecting unit 2 is formed by the endface of a light-receiving optical fiber 18c and is so provided that thedistance from the light-irradiating portion 19 differs from the distancefrom the light-irradiating portion 20.

FIG. 2 illustrates a specific example of the end face of a sensor probe50 having the light-irradiating portions 19, 20 of the light-irradiatingcircuit 1 and the photodetecting portion 21 of the light detecting unit.

Two light-emitting optical fibers and one light-receiving fiber arelinearly arrayed. The center-to-center distance between thelight-irradiating portion 20 formed by the end face of thelight-emitting optical fiber and the photodetecting portion 21 formed bythe end face of the light-receiving optical fiber is 0.26 mm, and thecenter-to-center distance between the light-irradiating portion 19formed by the end face of the light-emitting optical fiber and thephotodetecting portion 21 formed by the end face of the light-receivingoptical fiber is 0.50 mm. Thus, the optical fibers are provided so thatthese distances differ from each other. The fibers are fixed by an epoxyresin type bonding agent. Multicomponent glass with a core diameter of200 μm was used as the optical fiber. The peripheral portion of the endface of the sensor probe 50 is smoothly polished so as not to lose itslight transmissivity and in order to prevent clotting of blood. Thoughthe above-described sensor probe has the single photodetecting portion21 in order to make the sensor probe small in size, the invention is notlimited to this arrangement and a plurality of the photodetectingportions 21 can be provided.

FIG. 3 illustrates a state in which the sensor probe 50 is attached to aconnector 56 capable of being mounted in an extracorporeal circulatingcircuit (not shown) of an artificial lung, by way of example. Theconnector 56 has port 58, which is for attaching the sensor probe 50,projecting outwardly from a point midway along the axial length of theconnector. The end face of the sensor probe 50 is worked so that theinner wall surface of the connector 56 and the end face of the sensorprobe 50 will be substantially flush when the probe is attached to theconnector 56. This is so that the blood flowing through the connector 56will not be disturbed.

The detecting unit 2 has a photodiode 16 and a detecting amplifier 23which receive the light detected by the photodetecting portion 21 andtransmitted by the light-receiving optical fiber 18c. The photodiode 16generates a current conforming to the intensity of the light signal.This current is converted into a voltage signal by the detectingamplifier 23. The detecting unit 2 has a signal separating circuit forseparating the voltage signal from the detecting amplifier 23 intosignals corresponding to the light-emission wavelengths of thelight-emitting diodes 11, 12, 13. The signal separating circuit isconstituted by an analog switch 24, capacitors 25, 26, 27 and bufferamplifiers 28, 29, 30.

The analog switch 24 has three switches SW1, SW2, SW3 turned "ON and"OFF" by a signal from the pulse generator 14. For example, when thelight emitting diode 11 emits light, the signal from the pulse generator14 is applied to the analog switch 24 so that only SW1 assumes the "ON"state. As a result, the voltage signal from the detecting amplifier 23is applied to the capacitor 25 to produce a mean signal voltage acrossthe ends of the capacitor 25. This indicates the intensity of thereflected light of wavelength λ₁, in which the light is emitted by thelight-emitting diode 11, irradiates the blood from the light-irradiatingportion 20, is reflected from the blood and then received by thephotodiode 16 via the photodetecting portion 21. The mean signal voltageis continuously outputted through the buffer amplifier 28 to form asignal I₁ indicative of reflected-light intensity. Similarly, a likeoperation is performed by a combination of the light-emitting diode 12,SW2 of the analog switch 24, capacitor 26 and buffer amplifier 29,whereby a signal I₂ indicative of the reflected-light intensity ofwavelength λ₂ from light-emitting diode 12 is outputted. Further, a likeoperation is performed by a combination of the light-emitting diode 13,SW3 of the analog switch 24, capacitor 27 and buffer amplifier 30,whereby a signal I₃ indicative of the reflected-light intensity ofwavelength λ₂ from light-emitting diode 13 is outputted.

Further, the detecting unit 2 has a processor for the reflected-lightintensity signals I₁, I₂, I₃ outputted by the signal separating circuit.The signal processor has an analog-digital converter 31 for convertingthe reflected-light intensity signals I₁, I₂, I₃ into digital signals,and a mean value calculating unit 32 for computing mean values uponstoring the digitized reflected-light intensity signals I₁, I₂, I₃outputted by the analog-digital converter 31 a predetermined number (n)of times or within a predetermined period of time. The correcting unit 3which corrects for the influence of the hematocrit value has a firstcorrective value calculating unit 40, a second corrective valuecalculating unit 42 and a calculating unit 44 for calculating acorrected reflected-light intensity ratio.

The first corrective value calculating unit 40 has an arithmetic unitfor computing a reflected-light intensity ratio (I₂ /I₃) from onedigitized reflected-light intensity signal I₂ and one digitizedreflected-light intensity signal I₃ (e.g., digitized signals of thereflected-light intensity signals I₂, I₃ at the start of measurement)outputted by the mean value calculating unit 32. The output of the unitfor computing the reflected-light intensity ratio (I₂ /I₃) is deliveredas a first corrective value. In this case, therefore, the firstcorrective value calculating unit 40 is one which computes thereflected-light intensity ratio (I₂ /I₃) from the digitizedreflected-light intensity signals I₂, I₃. The first corrective value isa fixed corrective value until a new first corrective value is computed.

The construction of the first corrective value calculating unit 40 shownin FIG. 4 will now be described. Numeral 60 denotes a unit for computingthe reflected-light intensity ratio (I₂ /I₃), 62 a measurement valueinput unit for inputting a measurement value obtained by sampling bloodand measuring the hemoglobin concentration of the blood, and 63 an Hbcalibration curve recorder for storing the following referencecorrelation function h(x):

    h(x)=b.sub.2 ·x.sup.2 +b.sub.1 ·x+b.sub.0

[where x=I₂ /I₃, and h(x) is referred to as an Hb calibration curvehereinafter). This function is a higher-order correlation curve (e.g., asecond-degree regression curve) calculated from I₂ /I₃, which isobtained from several kinds of blood, regarding animal species, the sameas the blood which has already undergone measurement, and from thehemoglobin concentration Hb. Numeral 64 denotes an inverse functiong(Hb) memory for storing the inverse function g(Hb) of h(x). Numeral 65designates an arithmetic unit which uses the inverse function g(Hb) tocalculate a reflected-light intensity ratio [I₂ /I₃ ]_(s) correspondingto the hemoglobin concentration inputted by the measurement value inputunit 62. Numeral 66 represents an arithmetic unit for calculating

    (I.sub.2 /I.sub.3)/[I.sub.2 /I.sub.3 ].sub.s (=A)

from [I₂ /I₃ ]_(s), which is outputted by the arithmetic unit 65, and(I₂ /I₃), which is outputted by the arithmetic unit 60 that computes thereflected-light intensity ratio (I₂ /I₃) from the single digitizedreflected-light intensity signal I₂ and single reflected-light intensitysignal I₃ outputted by the mean value calculating unit 32. Numeral 67represents a hemoglobin concentration reference value (Hb') input unitfor inputting a reference value of hemoglobin concentration. Numeral 68denotes an arithmetic unit for calculating a reflected-light intensityratio function g(Hb') from the Hb calibration curve outputted by the Hbcalibration curve memory 63 and the hemoglobin concentration referencevalue (Hb') (e.g., a hemoglobin concentration of 15%). Numeral 69denotes an arithmetic unit for calculating the first corrective value

    X=[I.sub.2 /I.sub.3 ].sub.Hb=Hb' =A×g(Hb')

from A outputted by the arithmetic unit 66 and the reflected-lightintensity ratio function g(Hb'), which is obtained from thereflected-light intensity ratio g(Hb') arithmetic unit 68. In this casealso the first corrective value is a fixed corrective value until a newfirst corrective value is calculated.

The foregoing description relates to a case in which the apparatus isprovided with the Hb calibration curve memory 63, hemoglobinconcentration reference value (Hb') input unit 67 and the arithmeticunit 68 for calculating the reflected-light intensity ratio g(Hb') fromthe hemoglobin concentration reference value (Hb') (e.g., a hemoglobinconcentration of 15%) obtained from the Hb calibration curve of the Hbcalibration curve memory 63. However, the Hb calibration curve memory63, hemoglobin concentration reference value (Hb') input unit 67 and thearithmetic unit 68 for calculating the reflected-light intensity ratiog(Hb') can be deleted by fixing the hemoglobin concentration referencevalue (Hb') at, e.g., a hemoglobin concentration of 15% beforehand, andreplacing these units with a memory which stores the value ofreflected-light intensity g(Hb') calculated from the Hb calibrationcurve prevailing at this time (i.e., when the hemoglobin concentrationis 15%).

The first corrective value signal X (=[I₂ /I₃ ]_(Hb=Hb')) outputted bythe first corrective value calculating unit 40 enters the secondcorrective value calculating unit 42 along with the digitizedreflected-light intensity signal [I₃ ] outputted continuously by themean value calculating unit 32. The second corrective value calculatingunit 42 calculates a second corrective value C₁, based on the followingequation, using a previously stored constant C₀ :

    C.sub.1 =C.sub.0 ×[I.sub.3 ]×[I.sub.2 /I.sub.3 ].sub.Hb=Hb'

The second corrective value signal C₁ outputted by the second correctivevalue calculating unit 42 enters the corrected reflected-light intensityratio calculating unit 44 along with the digitized reflected-lightintensity signals [I₁ ], [I₂ ] outputted continuously by the mean valuecalculating unit 32. The calculating unit 44 computes a correctedreflected-light intensity ratio R_(s) from each of the foregoing signalsin accordance with the following equation:

    R.sub.s =([I.sub.1 ]-C.sub.1)/([I.sub.2 ]-C.sub.1)

The oxygen saturation calculating unit 4 stores a reference correlationfunction f(x), x=R_(s)

    f(x)=a.sub.3 ·R.sub.s.sup.3 +a.sub.2 ·R.sub.s.sup.2 +a.sub.1 ·R.sub.s +a.sub.0 (=SO.sub.2)

obtained by a third order regression of a correlation curve between thecorrected reflected-light intensity ratio R_(s) (=([I₁ ]-C₁)/([I₂ ]-C₁))of data from several types of blood measured in advance, and the degreeof oxygen saturation at this time. The calculating unit 4 computes thedegree SO₂ of oxygen saturation from the corrected reflected-lightintensity ratio R_(s) outputted by the corrected reflected-lightintensity ratio calculating unit 44. The constant C₀ of the secondcorrected value C₁ indicates the variance in the data regarding thereference correlation function f(x) in the form of a standard deviationand is decided in such a manner that this value is minimized.

The signal outputted by the oxygen saturation calculating unit 4 isdisplayed by the display unit 5. It will suffice if the latter is meanscapable of providing an external indication of the measured value.Well-known means can be used, such as a cathode-ray tube, printer,liquid-crystal display unit or recorder.

A second embodiment of the present invention will now be described usingFIG. 5.

An apparatus for measuring the degree of oxygen saturation in thisembodiment includes the light-irradiating circuit 1, the detecting unit2 for detecting the intensity of light reflected from blood irradiatedwith light from the light-irradiating circuit 1, a correcting unit 103,the unit 4 for calculating the degree of oxygen saturation using theoutput of the correcting unit 103, and the display unit 5 for displayingthe output of the oxygen saturation calculating unit 4.

The light-irradiating circuit 1, detecting unit 2, oxygen saturationcalculating unit 4 and display unit 5 are the same as those shown inFIGS. 1 through 3. The correcting unit 103, which differs from theforegoing correcting unit, will now be described.

The correcting unit 103 has a first corrective value calculating unit140, the second corrective value calculating unit 42 and the calculatingunit 44 for computing a corrected reflected-light intensity ratio. Thecalculating unit 140 has a construction different from that shown inFIG. 1.

As shown in FIG. 6, the first corrective value calculating unit 140comprises the Hb calibration curve memory 63 which stores the followingreference correlation function h(x):

    h(x)=b.sub.2 ·x.sup.2 +b.sub.1 ·x+b.sub.0

[where x=I₂ /I₃, and h(x) is referred to as an Hb calibration curvehereinafter), this function being a higher-order correlation curve(e.g., a second-order regression curve) calculated from I₂ /I₃, which isobtained from several kinds of blood of animal species the same as theblood which has already undergone measurement, and from the hemoglobinconcentration Hb, the hemoglobin concentration reference value (Hb')input unit 67, and the arithmetic unit 68 for calculating thereflected-light intensity ratio function g(Hb'), which serves as thefirst corrective value, based on the hemoglobin concentration referencevalue (Hb') (e.g., a hemoglobin concentration of 15%) in accordance withthe Hb calibration curve (reference correlation function) outputted bythe Hb calibration curve memory 63. The Hb calibration curve memory 63,hemoglobin concentration reference value input unit 67 andreflected-light intensity ratio calculating unit 68 are the same asthose described with reference to the block diagram of FIG. 4. Thoughthe first corrective value calculating unit 140 has been described withregard to a case in which the apparatus is provided with the Hbcalibration curve memory 63, hemoglobin concentration reference value(Hb') input unit 67 and the arithmetic unit 68 for calculating thereflected-light intensity ratio function g(Hb'), the Hb calibrationcurve memory 63, hemoglobin concentration reference value input unit 67and the arithmetic unit 68 can be deleted by fixing the hemoglobinconcentration reference value (Hb') at, e.g., a hemoglobin concentrationof 15% beforehand, and adopting a memory which stores the value ofreflected-light intensity g(Hb') function calculated from the Hbcalibration curve prevailing at this time (i.e., when the hemoglobinconcentration is 15%), just as in the case of FIG. 1.

The reflected-light intensity ratio function g(Hb') (=[I₂ /I₃]_(Hb=Hb')) outputted by the calculating unit 68 which computes thereflected-light intensity ratio function g(Hb') of the first correctivevalue calculating unit 140 enters the second corrective valuecalculating unit 42 along with the digitized reflected-light intensitysignal [I₃ ] outputted continuously by the mean value calculating unit32. The second corrective value calculating unit 42 calculates a secondcorrective value C₁, based on the following equation, using a previouslystored constant C₀ :

    C.sub.1 =C.sub.0 ×[I.sub.3 ]×[I.sub.2 /I.sub.3 ].sub.Hb=Hb'

The second corrective value signal C₁ outputted by the second correctivevalue calculating unit 42 enters the corrected reflected-light intensityratio calculating unit 44 along with the digitized reflected-lightintensity signals [I₁ ], [I₂ ] outputted continuously by the mean valuecalculating unit 32. The calculating unit 44 computes a correctedreflected-light intensity ratio R_(s) from each of the foregoing signalsin accordance with the following equation:

    R.sub.s =([I.sub.1 ]-C.sub.1)/([I.sub.2 ]-C.sub.1)

The oxygen saturation calculating unit 4 has a memory which stores areference correlation function f(x), (x=R_(s))

    f(x)=a.sub.3 ·R.sub.s.sup.3 +a.sub.2 ·R.sub.s.sup.2 +a.sub.1 ·R.sub.s +a.sub.0 (=SO.sub.2)

obtained by a third-order regression of a correlation curve betweenR_(s) (=([I₁ ]-C₁)/([I₂ ]-C₁)) regarding data from several types ofblood measured in advance, and the degree of oxygen saturation at thistime. The calculating unit 4 computes the degree SO₂ of oxygensaturation from the corrected reflected-light intensity ratio R_(s)outputted by the corrected reflected-light intensity ratio calculatingunit 44. The constant C₀ of the second corrected value C₁ indicates thevariance in the data regarding the reference correlation function f(x)in the form of a standard deviation and is decided in such a manner thatthis value is minimized. The signal outputted by the calculating unit 4is displayed by the display unit 5.

A method of measuring the degree of oxygen saturation by the oxygensaturation measuring apparatus of the present invention will now bedescribed in accordance with an embodiment with reference to theflowcharts of FIGS. 7 through 9.

EMBODIMENT 1

In accordance with the embodiment shown in FIG. 7, a connector of theconfiguration shown in FIG. 3 to which the sensor probe of FIG. 2 hasbeen mounted is attached to a blood circuit at a step S1. Next, at stepS2, blood is successively irradiated with the light of the approximatewavelengths of 660 nm (λ₁) and 800 nm (λ₂) from the light-irradiatingportion 20 formed by the end face of the optical fiber of thelight-irradiating unit shown in FIG. 1, and with the light of theapproximate wavelength of 800 nm from the light-irradiating portion 19formed by the end face of the optical fiber. The intensity of lightreflected from the blood irradiated with each light beam from thelight-irradiating unit 1 is detected n times by the detecting unit 2. Atstep S3, the mean value of each reflected-light intensity detected ntimes is calculated and the digitized reflected-light intensity signalsI₁, I₂, I₃ are outputted.

It is determined at step S4 whether to correct the reflected-lightintensity ratio I₂ /I₃ as a correction for preventing the influence ofthe hematocrit value. The program proceeds to step S5 if the correctionis to be performed.

At step S5, the reflected-light intensity ratio (I₂ /I₃) is calculatedfrom one (the initially outputted) digitized reflected-light intensitysignal I₂ /I₃ outputted at step S3, and this is stored as the firstcorrective value [I₂ /I₃ ]_(Hb=Hb').

The second corrective value C₁ is obtained at step S6 in accordance withthe equation

    C.sub.1 =C.sub.0 ×[I.sub.3 ]×[I.sub.2 /I.sub.3 ] or

    C.sub.1 =C.sub.0 ×[I.sub.3 ]×[I.sub.2 /I.sub.3 ].sub.Hb=Hb'

from the first corrective value stored at step S5 or, when a correctionis not made at step S4, the uncorrected reflected-light intensity ratioI₂ /I₃, the digital reflected-light intensity signal [I₃ ] continuouslyoutputted at step S3, and the previously stored C₀ (0.23 in thisembodiment).

The corrected reflected-light intensity ratio R_(s) is obtained at stepS7 in accordance with the equation

    R.sub.s =([I.sub.1 ]-C.sub.1)/([I.sub.2 ]-C.sub.1)

from the second corrective value C₁ outputted at step S6 and thedigitized reflected-light intensity signals [I₁ ], [I₂ ] continuouslyoutputted at step S3. By using the corrected reflected-light intensityratio R_(s) outputted at step S7, the degree of oxygen saturation iscalculated at step S8 from the reference correlation function f(x),(x=R_(s))

    f(x)=a.sub.3 ·R.sub.s.sup.3 +a.sub.2 ·R.sub.s.sup.2 +a.sub.1 ·R.sub.s +a.sub.0 (=SO.sub.2)

{f(x)=-4.165R_(s) ³ +38.08R_(s) ² -136.0R_(s) +180.0 in this embodiment}obtained by a third-order regression of a correlation curve between thecorrected reflected-light intensity ratio R_(s) (=([I₁ ]-C₁)/([I₂ ]-C₁))of data from several types of blood measured in advance, and the degreeof oxygen saturation. The degree of oxygen saturation calculated at stepS8 is displayed on the display unit 5 at step S9. It is determined atstep S10 whether measurement is to be terminated. If measurement is notterminated, the program returns to step S2 and the measurement describedabove is repeated.

FIG. 10 shows the relationship between degree of oxygen saturation for anumber (n=79) of items of data using the method of embodiment 1 anddegree of oxygen saturation measured with an OSM2 hemoxymeter(manufactured by Radiometer) used for purposes of contrast. It was foundfrom these results that accurate measurement can be carried out, inwhich the value (x) of degree of oxygen saturation obtained inaccordance with this embodiment approximates a correlation coefficient=1(y=x), with respect to the value (y) of degree of oxygen saturationobtained using the OSM2 hemoxymeter, with the error (S.D.) also beingsufficiently small.

EMBODIMENT 2

In accordance with embodiment 2 shown in FIG. 8, the mean value of eachreflected-light intensity detected n times is calculated and thedigitized reflected-light intensity signals I₁, I₂, I₃ are outputted atsteps S21 through S23, just as at steps S1 through S3 of FIG. 7.

It is determined at step S24 whether to apply a correction to thehemoglobin concentration as a correction for preventing the influence ofthe hematocrit value. The program proceeds to step S25 or step S26 ifthe correction is to be performed. At step S26, the reflected-lightintensity ratio (I₂ /I₃) is calculated from one (the initiallyoutputted) of each of the digitized reflected-light intensity signalsI₂, I₃ outputted at step S23, whereby [I₂ /I₃ ] is calculated.

At step S25, blood to be measured is sampled to measure hemoglobinconcentration. The program then proceeds to step S27 to calculate thereflected-light intensity ratio [I₂ /I₃ ]_(s) corresponding to themeasured hemoglobin concentration from the inverse function of thestored Hb calibration curve h(x), namely ##EQU1## along with thereference correlation function h(x)

    h(x)=b.sub.2 ·x.sup.2 +b.sub.1 ·x+b.sub.0

In this embodiment, h(x)=-21.51x² +53.02x -7.912.

[where x=I₂ /I₃, and h(x) is referred to as an Hb calibration curvehereinafter). This function is a higher-order correlation curve (e.g., asecond-order regression curve) calculated from I₂ /I₃, which is obtainedfrom several kinds of blood and already measured and stored, and fromthe hemoglobin concentration Hb.

Next, from [I₂ ]/[I₃ ] outputted at step S26 and [I₂ /I₃ ]_(s) outputtedat step S27, the following ratio between these two is calculated at stepS28:

    ([I.sub.2 ]/[I.sub.3 ])/[I.sub.2 /I.sub.3 ].sub.s (=A)

The program then proceeds to step S29, at which the reflected-lightintensity ratio g(Hb') of the hemoglobin concentration reference value(Hb') (a hemoglobin concentration of 15%) is calculated from the storedHb calibration curve, and the first corrective value

    X=[I.sub.2 /I.sub.3 ].sub.Hb=Hb' =A×g(Hb')

is calculated from the foregoing and from A, which is outputted at stepS28.

The second corrective value C₁ is obtained at step S30 in accordancewith

    C.sub.1 =C.sub.0 ×[I.sub.3 ]×[I.sub.2 /I.sub.3 ] or

    C.sub.1 =C.sub.0 ×[I.sub.3 ]×[I.sub.2 /I.sub.3 ].sub.Hb=Hb'

from the first corrective value stored at step S29 or, when a correctionis not made at step S24, the uncorrected reflected-light intensity ratio[I₂ /I₃ ], the digital reflected-light intensity signal [I₃ ]continuously outputted at step S23, and the already stored constant C₀(0.26 in this embodiment).

The corrected reflected-light intensity ratio R_(s) is obtained at stepS31 in accordance with the equation

    R.sub.s =([I.sub.1 ]-C.sub.1)/([I.sub.2 ]-C.sub.1)

from the second corrective value C₁ outputted at step S30 and thedigitized reflected-light intensity signals [I₁ ], [I₂ ]

continuously outputted at step S23.

By using the corrected reflected-light intensity ratio R_(s) outputtedat step S31, the degree of oxygen saturation is calculated at step S32from the reference correlation function f(x), (x=R_(s))

    f(x)=a.sub.3 ·R.sub.s.sup.3 +a.sub.2 ·R.sub.s.sup.2 +a.sub.1 ·R.sub.s +a.sub.0 (=SO.sub.2)

{f(x)=-4.165R_(s) ³ +38.08R_(s) ² -136.0R_(s) +180.0 in this embodiment}obtained by a third-order regression of a correlation curve between thecorrected reflected-light intensity ratio R_(s) (=([I₁ ]-C₁)/([I₂ ]-C₁))of data from several types of blood measured in advance, and the degreeof oxygen saturation. The degree of oxygen saturation calculated at stepS32 is displayed at step S33. It is determined at step S34 whethermeasurement is to be terminated. If measurement is not terminated, theprogram returns to step S22 and the measurement described above isrepeated.

FIG. 11 shows the relationship between degree of oxygen saturationobtained according to embodiment 2 and degree of oxygen saturationmeasured with an OSM2 hemoximeter (manufactured by Radiometer) used forpurposes of contrast. It was found from these results that accuratemeasurement can be carried out, in which the value (x) of degree ofoxygen saturation obtained in accordance with the method of thisembodiment approximates a correlation coefficient=1 (y=x), with respectto the value (y) of degree of oxygen saturation obtained using the OSM2hemoximeter, with the error (S.D.) also being sufficiently small.

EMBODIMENT 3

In accordance with embodiment 3 shown in FIG. 9, the mean value of eachreflected-light intensity detected n times is calculated and thedigitized reflected-light intensity signals I₁, I₂, I₃ are outputted atsteps S41 through S43, just as at steps S1 through S3 of FIG. 7. It isdetermined at step S44 whether to calculate the first corrective value.The program proceeds to step S45 if the correction is to be performed.At step S45, the reflected-light intensity ratio g(Hb') of thehemoglobin concentration reference value (Hb') (a hemoglobinconcentration 15% in this embodiment) is calculated from the referencecorrelation function h(x)

    h(x)=b.sub.2 ·x.sup.2 +b.sub.1 ·x+b.sub.0

which here is h(x)=-69.60x² +100.1x-15.18 [where x=I₂ /I₃, and h(x) isreferred to as an Hb calibration curve hereinafter), then the firstcorrective value [I₁ /I₂ ]_(Hb=Hb') is calculated. This function is ahigher-order correlation curve (e.g., a second-order regression curve)calculated from I₂ /I₃, which is obtained from several kinds of bloodand already measured and stored, and from the hemoglobin concentrationHb.

The second corrective value C₁ is obtained at step 46 in accordance withthe equation

    C.sub.1 =C.sub.0 ×[I.sub.3 ]×[I.sub.2 /I.sub.3 ] or

    C.sub.1 =C.sub.0 ×[I.sub.3 ]×[I.sub.2 /I.sub.3 ].sub.Hb=Hb'

from the first corrective value stored at step S45 or, when a correctionis not made at step S44, the uncorrected reflected-light intensity ratio[I₂ /I₃ ], the digital reflected-light intensity signal [I₃ ]continuously outputted at step S43, and the previously stored C₀ (0.26in this embodiment).

Next, the corrected reflected-light intensity ratio R_(s) is obtained atstep S47 in accordance with the equation

    R.sub.s =([I.sub.1 ]-C.sub.1)/([I.sub.2 ]-C.sub.1)

from the second corrective value C₁ outputted at step S46 and thedigitized reflected-light intensity signals [I₁ ], [I₂ ] continuouslyoutputted at step S43.

By using the corrected reflected-light intensity ratio R_(s) outputtedat step S47, the degree of oxygen saturation is calculated at step S48from the reference correlation function f(x), (x=R_(s))

    f(x)=a.sub.3 ·R.sub.s.sup.3 +a.sub.2 ·R.sub.s.sup.2 +a.sub.1 ·R.sub.s +a.sub.0 (=SO.sub.2)

{f(x)=-4.165R_(s) ³ +38.08R_(s) ² -136.0R_(s) +180.0 in this embodiment}obtained by a third-order regression of a correlation curve between thecorrected reflected-light intensity ratio R_(s) (=([I₁ ]-C₁)/([I₂ ]-C₁))of data from several types of blood measured in advance, and the degreeof oxygen saturation.

The degree of oxygen saturation calculated at step S48 is displayed onthe display unit 5 at step S49. It is determined at step S50 whethermeasurement is to be terminated. If measurement is not terminated, theprogram returns to step S42 and the measurement described above isrepeated.

FIG. 12 shows the relationship between degree of oxygen saturationobtained according to embodiment 3 and degree of oxygen saturationmeasured with an OSM2 hemoximeter (manufactured by Radiometer) used forpurposes of contrast. It was found from these results that accuratemeasurement can be carried out, in which the value (x) of degree ofoxygen saturation obtained in accordance with the method of thisembodiment approximates a correlation coefficient=1 (y=x), with respectto the value (y) of degree of oxygen saturation obtained using the OSM2hemoximeter, with the error (S.D.) also being sufficiently small.

Measurement of hemoglobin concentration according to another embodimentof the present invention will now be described.

As described above on the basis of FIG. 13, the light-absorption(reflection) characteristic of blood varies depending upon absorptionand scattering due to pigments and particles in the blood, and thelight-absorption coefficient varies greatly depending upon the state ofbonding between hemoglobin and oxygen and the wavelength of theirradiating light. In particular, in the vicinity of a wavelength of 800nm, HbO₂ and Hbr intersect and the extinction characteristics are equal.

FIGS. 20 and 21 are plots showing the relationship between hemoglobinconcentration and reflected-light intensity. These are experimentalresults regarding blood samples taken from three different bodies andusing light of wavelength 800 nm. FIG. 20 shows results obtained wherethe distance between the received light and emitted light is 0.25 mm,and FIG. 21 shows results obtained where the distance between thereceived light and emitted light is 0.50 mm. It should be noted thatthese measurements of reflected-light intensity are results obtainedupon previously calibrating each reflected-light intensity to apredetermined value using a white reflector.

FIG. 22 shows the relationship between the ratio I₁ /I₂ and hemoglobinconcentration, where I₁ is the reflected-light intensity when thedistance between the received light and emitted light is 0.25 mm, and I₂is the reflected-light intensity when the distance between the receivedlight and emitted light is 0.50 mm. FIGS. 20 and 21 show that eachreflected-light intensity is considerably influenced by differences inblood. As shown in FIG. 22, however, this influence can be mitigated bytaking the ratio of these intensities. Still, there is much influencefrom disparities in the scattering characteristic of blood.

Accordingly, the apparatus of the present invention is so adapted thatthe hemoglobin concentration of blood can be measured without theinfluence of differences among blood samples.

An apparatus for measuring hemoglobin concentration according to thepresent invention includes a light-irradiating circuit 100, a detectingunit 200 for detecting the intensity of light reflected from bloodirradiated with light from the light-irradiating circuit 100, acorrecting unit 300, a unit 400 for calculating hemoglobin concentrationusing the output of the correcting unit 300, and a display unit fordisplaying the output of the hemoglobin concentration calculating unit400. Portions the same as those shown in FIG. 1 are designated by likereference characters.

The light-irradiating circuit 100 has a first light-irradiating unit anda second light-irradiating unit for irradiating the blood with light ofa specific wavelength.

In the arrangement shown in FIG. 16, the first light-irradiating unitand the second light-irradiating unit are constituted by a firstlight-emitting source for emitting light of the specific wavelength, asecond light-emitting source for emitting light of the specificwavelength, and a light-irradiating unit for irradiating the blood withthe light from each of the light-emitting sources.

More specifically, the light-irradiating circuit 100 comprises alight-emitting source and a light-irradiating unit for irradiating theblood with light from the light-emitting source. The light-emittingsource comprises the two light-emitting diodes 12, 13 which emit lighthaving a wavelength of about 800 nm (λ₂). The light-emitting diodes 12,13 are arranged so as to emit light alternately by being driven througha driver circuit 115 to which pulses of a predetermined interval andpulse width are applied by a pulse generator 114 so as not to overlap intime. The light emitted by the light-emitting diode 12 passes throughthe light-emitting optical fiber 18a to irradiate the blood from thelight-irradiating portion 20 formed by the end face of the optical fiber18a. By adopting such an arrangement, the apparatus can be made small insize. Further, the light emitted by the light-emitting diode 13 passesthrough the light-emitting optical fiber 18b to irradiate the blood fromthe light-irradiating portion 19 formed by the end face of the opticalfiber 18b.

The invention is not limited to the arrangement shown in FIG. 16, for itis permissible to adopt an arrangement in which the light-irradiatingcircuit is composed of a shared light-emitting source for emitting lightof a specific wavelength, and two light-irradiating units forirradiating the blood from two different positions using the light fromthis light-emitting source.

The detecting unit 200 is for detecting the intensity of the light,which is emitted by the light-irradiating circuit 100, after the lightis reflected from the blood. In the arrangement shown in FIG. 16, thephotodetecting portion 21 of the detecting unit 200 is formed by the endface of the light-receiving optical fiber 18c and is so provided thatthe distance from the light-irradiating portion 19 differs from thedistance from the light-irradiating portion 20.

The specific example of the sensor probe 50 having theselight-irradiating portions 19, 20 and photodetecting portion 21 is asdescribed above with reference to FIG. 2.

The detecting unit 200 has the photodiode 16 and the detecting amplifier23 which receive the light detected by the photodetecting portion 21 andtransmitted by the light-receiving optical fiber 18c. The photodiode 16generates a current conforming to the intensity of the light signal.This current is converted into a voltage signal by the detectingamplifier 23. The detecting unit 200 has a signal separating circuit forseparating the voltage signal from the detecting amplifier 23 intosignals corresponding to the light-emission wavelengths of thelight-emitting diodes 12, 13. The signal separating circuit isconstituted by an analog switch 240, the capacitors 25, 26 and bufferamplifiers 28, 29.

The analog switch 240 has two switches SW1, SW2 turned "ON and "OFF" bya signal from the pulse generator 114. For example, when thelight-emitting diode 12 emits light, the signal from the pulse generator114 is applied to the analog switch 240 so that only SW1 assumes the"ON" state. As a result, the voltage signal from the detecting amplifier23 is applied to the capacitor 25 to produce a mean signal voltageacross the ends of the capacitor 25. This indicates the intensity of thereflected light of wavelength λ₂, in which the light is emitted by thelight-emitting diode 12, irradiates the blood from the light-irradiatingportion 20, is reflected from the blood and then received by thephotodiode 16 via the photodetecting portion 21. The mean signal voltageis continuously outputted through the buffer amplifier 28 to form asignal I₁ indicative of reflected-light intensity. Similarly, a likeoperation is performed by a combination of the light-emitting diode 13,SW2 of the analog switch 240, capacitor 26 and buffer amplifier 29,whereby a signal I₂ indicative of the reflected-light intensity ofwavelength λ₂ from light emitting diode 13 is outputted.

Further, the detecting unit 200 has processing means for thereflected-light intensity signals I₁, I₂ outputted by the signalseparating circuit. The signal processing means has an analog-digitalconverter 310 for converting the reflected-light intensity signals I₁,I₂ into digital signals, and a mean value calculating unit 320 forcomputing mean values upon storing the digitized reflected-lightintensity signals I₁, I₂ outputted by the analog-digital converter 310 apredetermined number (n) of times or within a predetermined period oftime.

The correcting unit 300 has a corrective coefficient calculating unit340, and a calculating unit 344 for computing a correctedreflected-light intensity ratio. As shown in FIG. 17, the correctivecoefficient calculating unit 340 preferably comprises an arithmetic unit360 for calculating a reflected-light intensity ratio (I₁ /I₂) from onedigitized reflected-light intensity signal I₁ and one digitizedreflected-light intensity signal I₂ outputted by the mean valuecalculating unit 320, a measurement value input unit 362 for inputting ameasurement value obtained by sampling blood and measuring thehemoglobin concentration of the blood, and a g(Hb) memory 364. Let

    h(R.sub.s)=b.sub.2 ·R.sub.s.sup.2 +b.sub.1 ·R.sub.s +b.sub.0

represent the reference correlation function h(R_(s)), which is ahigher-order correlation curve (e.g., a second-degree regression curve)calculated from I₁ /I₂, which is obtained from several kinds of blood ofanimal species and already measured, and from the hemoglobinconcentration Hb. Here, for example,

    h(R.sub.s)=-4.55·R.sub.s.sup.2 +37.8·R.sub.s -4.91

[where R_(s) =I₁ /I₂, and h(R_(s)) is referred to as an Hb calibrationcurve hereinafter). The g(Hb) memory 364 stores the inverse functiong(Hb) of the above, namely ##EQU2## The calculating unit furthercomprises an arithmetic unit 365 which uses the inverse function g(Hb)to calculate a reflected-light intensity ratio [I₁ /I₂ ]_(s)corresponding to the hemoglobin concentration inputted by themeasurement value input unit 362, and an arithmetic unit 366 forcalculating the corrective coefficient A in accordance with thefollowing equation:

    [I.sub.1 /I.sub.2 ].sub.s /(I.sub.1 /I.sub.2) (=A)

from [I₁ /I₂ ]_(s), which is outputted by the arithmetic unit 365, and(I₁ /I₂), which is outputted by the arithmetic unit 360.

The corrective coefficient A outputted by the corrective coefficientcalculating unit 340 enters a corrected reflected-light intensity ratiocalculating unit 344 along with the digitized reflected light-intensitysignals [I₁ ], [I₂ ] continuously outputted by the mean valuecalculating unit 340. The calculating unit 344 computes the correctedreflected light-intensity ratio R_(s) =A×[I₁ ]/[I₂ ] from theabovementioned signals.

In other words, the correcting unit 300 obtains the value of the ratioof (reflected-light intensity ratio calculated from referencecorrelation function) to (measured reflected-light intensity ratio) withregard to a known hemoglobin concentration, namely ##EQU3## andthereafter multiplies the successively measured reflected-lightintensity ratio by the value of this ratio, which serves as a correctivecoefficient. Thus, a so-called span calibration is performed based onthe known hemoglobin concentration.

The hemoglobin concentration calculating unit 400 stores the referencecorrelation function h(R_(s))

    h(R.sub.s)=b.sub.2 ·R.sub.s.sup.2 +b.sub.1 ·R.sub.s +b.sub.0

which is a higher-order correlation curve (e.g., a second-degreeregression curve) calculated from I₁ /I₂, which is obtained from severalkinds of blood of animal species and already measured, and from thehemoglobin concentration Hb. Here, for example,

    h(R.sub.s)=-4.55·R.sub.s.sup.2 +37.8·R.sub.s -4.91

[where R_(s) =I₁ /I₂, and h(R_(s)) is referred to as an Hb calibrationcurve hereinafter). The unit 400 calculates hemoglobin concentration,using the abovementioned equation of the Hb calibration curve, from thecorrected reflected-light intensity ratio RS outputted by thecalculating unit 344.

The signal outputted by the hemoglobin concentration calculating unit400 is displayed by the display unit 5. It will suffice if the latter ismeans capable of providing an external indication of the measured value.Well-known means can be used, such as a cathode ray tube, printer,liquid-crystal display unit or recorder.

A method of measuring the hemoglobin concentration by the hemoglobinconcentration measuring apparatus of the present invention will now bedescribed in accordance with an embodiment with reference to theflowchart of FIG. 18.

In accordance with the embodiment shown in FIG. 18, a connector of theconfiguration shown in FIG. 3 to which the sensor probe of FIG. 2 hasbeen mounted is attached to a blood circuit at a step S61. Next, at stepS62, blood is successively irradiated with the light of the approximatewavelength of 880 nm (λ₂) from the light-irradiating portions 19, 20formed by the end face of the optical fiber of the light-irradiatingunit shown in FIG. 16, and the intensity of light reflected from theblood irradiated with each light beam from the light-irradiating unit100 is detected n times by the detecting unit 200. At step S63, the meanvalue of each reflected-light intensity detected n times is calculatedand the digitized reflected-light intensity signals I₁, I₂ areoutputted.

It is determined at step S64 whether to apply a correction to thehemoglobin concentration. The program proceeds to step S69 when thecorrection is not carried out. When the correction is performed,however, the program proceeds to steps S65 and S66. At step S65, thereflected-light intensity ratio (I₁ /I₂) is calculated from one (theinitially outputted) of each of the digitized reflected-light intensitysignals I₁, I₂ outputted at step S63.

At step S66, blood to be judged is sampled to measure hemoglobinconcentration. The program then proceeds to step S67 to calculate thereflected-light intensity ratio [I₁ /I₂ ]_(s) corresponding to themeasured hemoglobin concentration from the inverse function g(Hb) of thereference correlation function h(R_(s))

    h(R.sub.s)=b.sub.2 ·R.sub.s.sup.2 +b.sub.1 ·R.sub.s +b.sub.0

which is a higher-order correlation curve (e.g., a second-degreeregression curve) calculated from the reflected light-intensity ratio(I₁ /I₂), which is obtained from several kinds of blood of animalspecies and already measured, calculated and stored, and from thehemoglobin concentration Hb. Here, for example,

    h(R.sub.s)=-4.55·R.sub.s.sup.2 +37.8 ·R.sub.s -4.91

[where R_(s) =I₁ /I₂, and h(R_(s)) is referred to as an Hb calibrationcurve hereinafter). Thus the inverse function g (Hb) is ##EQU4##

When the reflected-light intensity ratio (I₁ /I₂) is thus obtained, theprogram proceeds to step S68. Here, from [I₁ /I₂ ] outputted at step S65and [I₁ /I₂ ]_(s) outputted at step S66, the corrective coefficient ([I₁/I₂ ]_(s))/(I₁ /I₂) (=A), which is the ratio between the two, iscalculated.

It is determined at step S69 whether the corrective coefficient Acalculated at step S68 is to be used. If it is decided that thecorrective coefficient A is to be used, the program proceeds to stepS70, at which the corrected reflected-light intensity ratio R_(s) isobtained from R_(s) =A×[I₁ ]/[I₂ ] using the coefficient and thedigitized reflected-light intensity signals [I₁ ], [I₂ ] outputtedcontinuously at step S63. If the corrective coefficient A calculated atstep S68 is cot to be used, then the program proceeds to step S71, atwhich the reflected-light intensity ratio R is obtained from R=[I₁ ]/[I₂] using the digitized reflected-light intensity signals [I₁ ], [I₂ ]outputted continously at step S63.

Next, at step S72, using the corrected reflected-light intensity ratioR_(s) obtained at step S70 or the reflected-light ratio R_(s) obtainedat step S71, hemoglobin concentration is calculated using the referencecorrelation function h(R_(s))

    h(R.sub.s)=b.sub.2 ·R.sub.s.sup.2 +b.sub.1 ·R.sub.s +b.sub.0

which is a higher-order correlation curve (e.g., a second-degreeregression curve) calculated from I₁ /I₂, which is obtained from severalkinds of blood of animal species and already measured, calculated andstored, and from the hemoglobin concentration Hb. Here, for example,

    h(R.sub.s)=-4.55·R.sub.s.sup.2 +37.8·R.sub.s -4.91

[where R_(s) =I₁ /I₂, and h(R_(s)) is referred to as an Hb calibrationcurve hereinafter).

The hemoglobin concentration outputted at step S72 is displayed at stepS73, and it is determined at step S74 whether to terminate measurement.If measurement is not terminated, the program returns to step S62 andthe foregoing measurement is repeated.

FIG. 19 illustrates the relationship between hemoglobin concentrationobtained according to the embodiment and hemoglobin concentrationmeasured with an OSM2 hemoximeter (manufactured by Radiometer) used forpurposes of contrast. It was found from these results that accuratemeasurement can be carried out, in which the value (x) of hemoglobinconcentration obtained in accordance with the method of this embodimentapproximates a correlation coefficient=1 (y=x), with respect to thevalue (y) of hemoglobin concentration obtained using the OSM2hemoximeter, with the error (S.D.) also being sufficiently small.

INDUSTRIAL APPLICABILITY

Thus, as set forth above, the apparatus for measuring hemoglobinconcentration and the apparatus for measuring degree of oxygensaturation of the present invention are suited to continuous measurementof hemoglobin concentration in blood and degree of oxygen saturation ofhemoglobin.

What is claimed is:
 1. An apparatus for measuring a degree of oxygensaturation in blood, comprising:source means for emitting light at afirst and second wavelength (λ₁, λ₂), with a difference of a degree ofextinction between oxygenated hemoglobin and carbomonoxy hemoglobinbeing comparatively large at said first wavelength and small at saidsecond wavelength; first light-irradiating means having a firstlight-irradiating portion, and being coupled to said source means foralternately irradiating blood with light of said first or secondwavelength (λ₁, λ₂); second light irradiating means having a secondlight-irradiating portion, and being coupled to said source means forconstantly irradiating the blood with light of said second wavelength λ₂; detecting means, arranged such that the distance from the detectingmeans to said first light-irradiating means and the distance from thedetecting means to said second light-irradiating means differ, fordetecting intensities (I₁, I₂, I₃) of light reflected from the bloodirradiated with the light from each of the first and secondlight-irradiating portions of said first and second light-irradiatingmeans corresponding to their wavelength; memory means for storing an Hbcalibration curve; arithmetic means for calculating a reflected-lightintensity ratio function g(Hb') of blood having a reference value (Hb')of hemoglobin concentration by reference to said Hb calibration curvestored in said memory means; first corrective value calculating meansfor calculating a first corrective value (X) based on both areflected-light intensity ratio (I₂ /I₃)_(s)) from a blood with knownhemoglobin concentration and said reflected-light intensity ratiofunction, according to an equation X=g(Hb')×(I₂ /I₃)/(I₂ /I₃)_(s), tocorrect a ratio (I₂ /I₃) of detected reflected-light intensity (I₂) dueto irradiation with light of said second wavelength produced by saidfirst light-irradiating means versus detected reflected-light intensity(I₃) due to irradiation with light of said second wavelength produced bysaid second light-irradiating means; second corrective valuescalculating means for calculating a second corrective value (C₁) basedon said first corrective value (X), the reflected-light intensity (I₃)of light from the second light-irradiating means detected continuouslyby said detecting means, and a constant value (C₀), according to anequation C₁ =C₀ ×(I₃)×(X); reflected-light intensity ratio correctingmeans for correcting to remove an influence of hematocrit value and forcalculating a corrected reflected-light intensity ratio (R_(s)) based onsaid second corrective value (C₁), a reflected-light intensity ratio (I₁/I₂) of the detected reflected-light intensity (I₁) of light of saidfirst wavelength produced by the first light-irradiating means versusdetected reflected-light intensity (I₂) of light of said secondwavelength produced by the first light-irradiating means, according toan equation R_(s) =(I₁ -C₁)/(I₂ -C₁); and oxygen saturation degreecalculating means for calculating the degree of oxygen saturation inblood based on a correlation function (f(x)) using the correctedreflected light intensity ratio (R_(s)) outputted by said reflectedlight intensity ratio correcting means.
 2. An apparatus for measuring adegree of oxygen saturation according to claim 1, wherein said memorymeans stores a reference correlation function h(x) as said Hbcalibration curve: wherein

    h(x)=b.sub.2 x.sup.2 +b.sub.1 x+b.sub.0

and where x=I₂ /I₃, and b₀, b₁ and b₂ are constant values.
 3. Anapparatus for measuring a degree of oxygen saturation according to claim1, wherein said second corrective means calculates said second value C₁by using an equation:

    C.sub.1 =C.sub.0 ×(I.sub.3)×(X)

where C₀ is a constant value.
 4. An apparatus for measuring a degree ofoxygen saturation according to claim 1, wherein said oxygen degreecalculating means calculates the degree of oxygen saturation in bloodbased on the correlation function f(x):

    f(x)=a.sub.3 R.sub.s.sup.3 +a.sub.2 R.sub.s.sup.2 +a.sub.1 R.sub.s +a.sub.0

where a₀, a₁, a₂ and a₃ are constant values.
 5. An apparatus formeasuring a degree of oxygen saturation according to claim 1, whereineach of said first and second light-irradiating means includes anoptical fiber for transmitting light from said source means respectivelyto said first and second light-irradiating portions, each of said firstand second light-irradiating portions comprising an end face of saidoptical fiber.
 6. An apparatus for measuring a degree of oxygensaturation according to claim 1, wherein said detecting means includes aphotodetector, and a light-transmitting portion for transmitting lightfrom a photodetecting portion to said photodetector, said photodetectingportion comprising an end face of an optical fiber which forms thelight-transmitting portion.
 7. An apparatus for measuring hemoglobinconcentration in blood, comprising:source means for emitting light at aspecific wavelength (λ₂), with a difference of a degree of extinctionbetween oxygenated hemoglobin and carbomonoxy hemoglobin beingcomparatively small; first and second light-irradiating means havingfirst and second light-irradiating portions, respectively, and beingcoupled respectively to said source means for irradiating blood withlight of said specific wavelength (λ₂) from different directions;detecting means, arranged such that the distance from the detectingmeans to said first light-irradiating means and the distance from thedetection means to said second light-irradiating means differ, fordetecting intensities (I₁ /I₂) of light reflected from the bloodirradiated with the light from the first and second light-irradiatingportions of said first and second light-irradiating means; correctivecoefficient calculating means for calculating a corrective coefficient(A) based on a ratio of a ratio (I₁ /I₂) of the reflected-lightintensity (I₁) of light from said first light-irradiating means to thereflected-light intensity (I₂) of light from said secondlight-irradiating means to a ratio ((I₁ /I₂)_(s)) of intensities ofreflected-light from a blood with known hemoglobin concentrationirradiated by said first and second light-irradiating means, accordingto an equation A=((I₁ /I₂)_(s) /(I₁ /I₂)); reflected-light intensityratio correcting means for multiplying a reflected-light intensity ratio(I₁ /I₂) by said corrective coefficient (A) to obtain a correctedreflected-light ratio (R_(s)); and hemoglobin concentration calculatingmeans for calculating the hemoglobin concentration in blood based on acorrelation function h(R_(s)) using the corrected reflected-lightintensity ratio (R_(s)) outputted by said reflected light intensityratio correcting means.
 8. An apparatus for measuring a hemoglobinconcentration according to claim 7, wherein each of said first andsecond light-irradiating means has different light-irradiating portionsfor irradiating the blood with light from said source means fromdifferent directions.
 9. An apparatus for measuring a hemoglobinconcentration according to claim 7, wherein said corrective coefficientcalculating means includes memory means for storing an inverse functiong(HB), and arithmetic means for calculating a reflected-light intensityratio ((I₁ /I₂)_(s)) from blood with known hemoglobin concentrationusing both the inverse function g(Hb) and a reference value ofhemoglobin concentration.
 10. An apparatus for measuring a hemoglobinconcentration according to claim 7, wherein said reflected-lightintensity ratio correcting means calculates said correctedreflected-light intensity ratio (Rs) according to an equation:

    Rs=A×(I.sub.1 /I.sub.2)={(I.sub.1 /I.sub.2).sub.s /(I.sub.1 /I.sub.2)}×(I.sub.1 /I.sub.2).


11. An apparatus for measuring a hemoglobin concentration according toclaim 7, wherein said hemoglobin concentration calculating meanscalculates the hemoglobin concentration in blood based on thecorrelation function:

    H(Rs)=-4.55 R.sub.s.sup.2 +37.8 R.sub.s -4.91.


12. An apparatus for measuring a hemoglobin concentration according toclaim 7, wherein said detecting means includes a photodetector, and alight-transmitting portion for transmitting light from a photodetectingportion to said photodetector, said photodetecting portion comprising anend face of an optical fiber which forms the light-transmitting portion.